Hydrocarbon conversion in pebble heaters



Dec. 5, 1950 H. A. DUTCHER HYDROCARBON CONVERSION IN PEBBLE HEATERS mm m0 5.5; 0H:

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INVENTOR. HARRIS A. DUTCHER Br WM ATTORNEYS Patented Dec. 5, 1950HYDROCARBON CONVERSION IN PEBBLE HEATERS Harris A. Dutcher,Bartlesvllle, kla., assignor to Phillips Petroleum Company, acorporation of- Delaware Application July 8, 1946, Serial No. 681,967

This invention pertains to an improved process for conversion ofhydrocarbons.

In hydrocarbon conversion processes involving cracking, dehydrogenation,reforming, etc., more or less carbonaceous matter, such as tar or coke.is deposited in the conversion zone. When operating with a stationarycatalyst bed, it is necessary to periodically burn oil the carbon,thereby reducing conversion time and the rate of production. In order toovercome this'disadvantage and obviate periodic on-stream operation, aprocess has been devised wherein the conversion reaction is carried onin a zone thru which a moving mass of hot heat-transfer material flows,supplying suflicient heat to meet conversion requirements. In some casesthe heat-transfer particles are catalytic to the conversion reaction andin others they are relatively inert. In other cases a mixture ofcatalytic and non-catalytic particulate refractory materials is utilizedin a mixed stream.

During operation according to the process just described more or lesscarbon is formed on the particulate material circulating thru theconversion zone. This particulate material, which may be in the form ofsmall pebbles, becomes cooled in the conversion zone and must bereheated before returning it to the conversion zone.- During thereheating of the pebbles with hot combustion gas containing a regulatedamount of oxygen, carbonaceous deposit on the pebbles is removed bycombustion. But during this reheating and carbon-removing step, it isdifficult to control the temperature thruout the pebble mass, resultingin uneven and excessive temperatures which sometimes cause pebblebreakage, fusion, channeling, etc. This is because of uneven carbondistribution and uneven heating generated by combustion thereof.Excessive and uneven heating of pebbles is detrimental to pebbles inmany instances, especially when catalytic materials are incorporatedtherein, and results in ineflicient temperature control of theconversion process, itself. I

In normal pebble heater operation at conversion temperatures of theorder of about l2 00 to 3000 F., the pebbles leaving the conversion zoneand entering the elevator are too hot to be handled with ordinary highcarbon steel elevator or transfer equipment and require special, ratherexpensive alloy equipment.

It is an important object of the present invention to provide a processfor the conversion of hydrocarbons, using pebble heater technique, whichpermits the removal of carbonaceous de- 12 Claims. (Cl. 196-45) positfrom the pebbles with improved control of temperatures and more uniformheating of pebbles in the system.

Another, object of the invention is to provide a process for theconversion of hydrocarbons at elevated temperatures, using pebble heatertechnique, which permits the use of ordinary carbon steel elevatorequipment in place of the conventional expensive high temperaturealloys.

A further object of this invention is to provide a continuous, efiicientprocess for the conversion of hydrocarbons in which normal carbonaceousdeposit from the conversion reaction is utilized as at least a portionof the fuel consumed in producing the heat requirements of the process.

It is also an object of this invention to provide a process for theconversion of hydrocarbons which utilizes sensible heat of elfluentsfrom the conversion zone as a portion of the heat requirements of theprocess.

Other objects, such as the conservation of pebbles, will become apparentfrom a consideration of the accompanying disclosure.

According to this invention a fluent mass of hot, small, refractoryelements, called pebbles, are continuously flowed by gravity thru a.series of vertically extending zones including a pebble heating zone, aconversion zone, and a pebble cooling zone; and the pebbles aresimultaneously contacted in each zone by a gas having the desiredfunction. These pebbles are preferably spherical and relatively uniformin size but may be rod-shaped or irregular in shape and size. Spheres ofabout 5" to 1" in diameter may be utilized but spheres of from about A"to /2" in diameter are most practical. These pebbles must be able towithstand temperatures up to about 3500 F. in some cases, so must besufficiently refractory at the anticipated highest temperature in thepebble heating chamber in a given conversion process. Pure aluminapebbles which have been heated to about 3500 F. for a substantial periodmake excellent pebbles. These may be utilized as is, or afterimpregnation with more active catalyst material. Pebbles comprisingberyllia, Carborundum, mullite, periclase, and zirconia make excellentpebbles in some processes when properly fired. Alumina in pure form whenstabilized with a small amount (less than 5%) of an alkali or alkalineearth metal oxide and impregnated with a metal oxide from groups 'V orVI of the periodic table makes an excellent catalytic pebble capable ofwithstanding moderately high temperatures, such as 2500 F., suitable fordehydrogenation, cracking, and reforming of hydrocarbons.

Pebbles descending thru the pebble heating chamber are contacted by astream ofhot combustion gas, preferably countercurrently, at atemperature and flow rate regulated to insure heating of the pebbles toa temperature substantially above a predetermined conversion temperaturein the range of about 1500 to 3000 F. Pebble temperatures at least 100F. above conversion temperature are desirable and they mayadvantageously be several hundred degrees above. Since the amount ofheat delivered in the conversion zone is dependent upon the differencebetween pebble inlet temperature and pebble outlet temperature and thequantity of pebbles passed thru this zone, the temperature of conversioncan be regulated by controlling these factors. By utilizing high pebbleinlet temperatures to'the conversion chamber and relatively rapid pebbleflow, extremely large heat requirements can be met.

Hot pebbles flowing thru the conversion chamber are continuouslycontacted with a gaseous stream of a selected hydrocarbon feed,preferably countercurrently, at a flow rate designed to produce thedesired amount of conversion. It is desirable to preheat the feed to atemperature substantially below conversion temperature but suflicientiyhigh that there is not too great a gradient in pebble temperature in theconversion chamber. By correlating the pebble inlet temperature, rate ofpebble flow, feed preheat temperature, and feed flow rate, desirableconversion temperatures up to about 3200 F. are feasible.

In hydrocarbon conversion reactions, involving cracking,dehydrogenation, reforming, etc., carbonaceous material is deposited inthe reaction zone and when operating in pebble heater apparatus this islargely deposited on the pebbles. According to the invention, the pebblestream, carrying a substantial amount of carbon, descends thru a thirdchamber directly below the conversion chamber and is there continuouslycontacted with a stream of steam passing upwardly thru the pebblestream. When operating under conditions which result in high pebble exittemperatures from the conversion chamber, such as about 1300 F. to 2600F., it is feasible to react the steam with the carbonon the pebbles toproduce water gas. This step in the process not only converts the carbonto utilizable fuel for heating in the pebble heating zone, withoutoverheating the pebbles. but also reduces the pebble exit temperaturefrom this chamber so that pebbles can be transferred and elevated inordinary carbon steelequipment. The lower part of this pebble coolingchamber serves to raise the temperature of the steam to such a degreethat the water gas reaction is initiated in the upper region of thechamber. By proper correlation of the temperature and quantity of steamadmitted, the inlet pebble temperature, and' pebble flow rate, thepebble stream can be reduced to a temperature at which the necessity forexpensive high-temperature alloys in elevator equipment is obviated.This temperature should be in the range of about 500 to 900 F. Theamount of steam admitted may well be in excess of that required toremove the carbon from the pebbles since excess steam merely serves as atempering fluid in both the pebble cooling zone and the pebble heatingzone. In cases where it is desirable to pass less steam into thecombustion chamber than is present in efliuent may be passed thru awaste heat boiler or condenser to remove a por.ion of the steam therein.In cases where it is not desirable to utilize the eflluents containingwater gas in the combustion zone of the pebble heater, this eflluent gasmay be disposed of in any desirable manner. Such may be the case whenonly a slight deposition of carbon is taking place in the conversionzone. I

In operating at extremely high conversion temperatures, it is oftendesirable to'pass the pebble stream thru a preheating chamber beforeallowing it to pass into the heater proper and there contact it with thehot eiiluents from the conversion zone. This step utilizes aconsiderable portion of the sensible heat of the product gases anddesirably cools those gases before they pass to separation means. Whenselectively cracking or dehydrogenating it adds considerably to yield toquickly quench the eilluents from the conversion zone. This may beaccomplished by injection of cooling fluids into the etlluent line toreduce the temperature to a point at which further reaction issubstantially prevented. Quenching to about 800 or 900 F. will usuallysufflce and the quenched stream still has considerable utility inpreheating the pebble stream which may enter this chamber at atemperature as low as about 450 F.

For a more complete understanding of the invention, reference'may be hadto the accompanying drawing of which Fig. 1 is a diagrammatic showing ofa desirable arrangement of equipment for performing the process of theinvention. Fig. 2 is a diagrammatic showing of apparatus arranged forperforming that embodiment of the invention involving preheating of thepebble stream.

Referring to Figure 1, a fluent mass of pebbles l0, substantiallyfilling heat-insulated chambers l2, l3, and I4, and necks I5, l6, l1,and I8 descends by gravity thru the various chambers of the apparatusand passes thru star valve 2| (or other feeder device) in chute l9 toelevator 22. Elevator 22 transfers the pebbles at'a predetermined rateto chute 23 from which they again enter inlet neck [5 and flow thru thesystem. By regulation OLZL Q rate of operation of feeder valve 2| acontiguous column of pebbles is maintained thruout the apparatus belowchute 23 so that there are no unnecessary voids in the chambers andnecks connecting them. Regulation of the flow of pebbles may also beattained by utilizing a variable speed motor on the elevator, therebycontrolling the rate of return of pebbles to the pebble inlet chute.

As pebbles flow thru chamber l2, they are heated to a temperature atleast F. above a predetermined conversion temperature by contact with astream of hot combustion gas from furnace or burner 24. Fuel and air arefed into-,

' p asses up t h ru the des cending pebblgstrgam, it

substantial conversion takes place before leaving chamber l3 via line 33and heat-exchanger 2! which serves to preheat either air or fuel forcombustion purposes. Line 34 controlled by valve 33 introduces quenchingfluid to line 33. The pebble stream emerging from chamber l3 passes thruneck l1 into pebble cooling chamber I4 and is contacted by a stream ofsteam fed in thruline 38 controlled by valve 31 and passing thruheatexchanger 3|. Auxiliary line 38 controlled by valve 38 is utilizedto supplement and temper the steam admitted thru line 38. Thetemperature of steam passed thru line 36 can be increased to any degreerequired in chamber ll by heat-exchange with flue gas in exchanger 3 I.Steam admitted to chamber ll contacts the hot carbon coated pebblesdescending thru the chamber and effects the water gas reaction,producing CO and H: which passes via line 28 to fuel line 25, supplyingburner or furnace 24.

Operation at pressures varying only slightly from atmospheric such as0.5 to 5 p. s. i. g. are preferred, but other pressures either above orbelow atmospheric may be utilized with varying efficiency. Maintenanceof substantially equal pressures in the various pebble chambers resultsin less gas flow between chambers than otherwise. In some types ofconversion it may be desirable to operate with a non-deleteriousblocking gas, such as steam, in necks l5, l6. I1, and I8, supplied vialines ll, 42, 43, and M, respectively. The same or different gases maybe used in these necks.

The arrangement of apparatus shown in Fig. 2 is similar to that of Fig.l, but an additional pebble chamber is utilized above pebble heater i2.designated as pebble preheating chamber H. Pebbles enter chamber l Ifrom neck 45 and chute 23 (leading from the elevator not shown) and arecontacted therein with hot eiiluents, either quenched or unquenched,from conversion chamber l0. passing in via line 33 and leaving via line61. Line 66 admits steam or other blocking gas to neck 65. Theembodiment of the invention illustrated in Fig. 2 makes it possible toattain extremely high conversion temperatures with sharp heating in theconversion zone without "pushing the pebble heater proper and withhigher heating eifl iency.

By way of illustration a feed consisting of 5% methane, 80% ethane, andpropane by volume is cracked in a two-chamber pebble heater at about1600 F. with a reaction time of 0.2 se ond. The efiluent from this firststage has the followin enmDnsition in volume per cen 29.8 H2 15.1 CH4.36.0 C'iH4. 13.5 CzHs, 1.2 CJHG, 2.0 03H. 2.4 C4s and heavier.

The eiilnent resulting from cracking at 1600 F. is pa sed thru theconversion chamber of a threechamber pebble heater apparatus, accordingto the invention, o erating at a conversion temperature of about 2500 F.and a reaction time of 0.5 se ond. using alumina spheres as pebbles.During this con ersion, the pebble stream enters the pebble heatingchamber at about 450 F., is contacted by a stream of combustion gasentering the lower portion of the chamber at about 3200 F. and leavingat about 800 F., and is brought up to a temperature of about 2800 F.Durin the descent thru the conversion zone, this 2800 F. stream ofpebbles drops in temperatureto about 1800 F. as a result of heating andconverting the feed stream which enters the lower portion of the chamberat about 1600 F. While descending thru the pebble cooling chamber, the

pebble stream, carrying'carbon to the extent of about 5% of the feed byweight, is contacted with a stream of steam entering the lower portionof the chamber at about 240 F. About 5 pounds of steam are fed into thepebble cooling chamber for each pound of carbon entering this chamberwith the pebble stream. The pebbles emerge from this chamber at about600 F. and are substantially free of carbonaceous material. Theeflluent, containing water gas and steam and at a temperature of about1200 F., is passed to the combustion chamber as fuel. Pebbles at about600 F. are transferred in ordinary carbon steel elevator equipment tothe inlet to the pebble heating chamber.

The product from the first cracking operation is converted, according tothe invention, into the following products by volume per cent: 43.6 Hz,16.5 CH4, 20.0 CzHz, 11.6 CzH4, 2.5 CzHe, and 5.8 C4s and heavier(including coke).

During the operation, removal of carbon from pebbles is substantiallycomplete and little difflculty in obtaining rather uniform temperaturesis experienced. This is in contrast to conven-- ticnal removal of carbonfrom catalyst or pebbles in the heating chamber by oxidation, withconcomitant localized overheating of the heat-transfer material.

Various modifications of the invention will become apparent to thoseskilled in the art. The illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A continuous process for conversion of hydrocarbons at elevatedtemperatures which comprises continuously flowing a fluent contiguous mas of hot refractory pebbles thru a series of substantiall verticallyextending zones comprising a pebble heating zone, a pebble coolin zonepositioned below said nebble heating zone, and a conversion zonepositioned intermediate said zones and communicating therewith thrurela-' tively narrow zones, each of said zones being substantiallyfilled with said pebbles and permitting relatively unrestricted fiow ofpebbles therethru; continuously contacting that portion of saidcontiguous mass of pebbles flowing thru said pebble heating zone with astream of hot combustion gas at a temperature and flow rate regulated toinsure heating of said pebbles to a temperature substantially above apredetermined conversion temperature; continuously contacting thatportion Of said contiguous mass of pebbles flowing thru said conversionzone with a stream of hydrocarbon gas at a flow rate regulated to insureheatin of said hydrocarbon gas to said conversion temperature andsubstantial conversion thereof to desired products whereb carbonaceousmaterial is deposited on said pebbles; continuously contacting thatportion of said contiguous mass of pebbles flowing thru said pebblecooling zone with a stream of superheated steam at a temperature andflow rate regulated to insure substantial removal of carbonaceousdeposit from said pebbles by the Water gas reaction and substantialcooling thereof with concomitant production of water gas; continuouslyburning said water gas with other fuel to produce said hot combustiongas; continuously removing pebbles from said pebble cooling zone;continuously introducing pebbles to said pebble heating zone; andcontinuously recovering efliuents from said conversion zone.

2. The process of claim 1 in which pebble flow and gas flow in pebbleheating zone, conversion zone, and pebble cooling zone arecountercurrent.

3. The process of claim 1 in which conversion temperature is in therange of about 1500 to 3000 F. and pebble exit temperature from theconversion zone is in the range of about 1300"- 2600" F.

4. The process of claim 1 in which the pebbles are catalytic withrespect to the conversion reaction.

5. A continuous process for conversion of hydrocarbons to more desirablehydrocarbons at elevated temperatures which comprises continuouslyflowing a fluent contiguous mass of hot refractory pebbles thru a seriesof substantially vertically extending zones comprising a pebble heatingzone, a pebble cooling zone positioned below said pebble heating zone,and a conversion zone positioned intermediate said zones andcommunicating therewith thru relatively narrow zones, each of said zonesbeing substantially filled with said pebbles and permitting relativelyunrestricted flow of pebbles therethru; continuously contacting thatportion of said contiguous mass of pebbles flowing thru said pebbleheating zone with a stream of hot combustion gas at a temperature andflow rate regulated to insure heating of said pebbles to a temperaturesubstantially above a predetermined conversion temperature in the rangeof 1500 to 3000 F.; continuously contacting that portion of saidcontiguous mass of pebbles flowing thru said conversion zone with astream of hydrocarbon gas at a flow rate regulated to insure heating ofsaid hydrocarbon gas to said conversion temperature and substantialconversion thereof to desired hydrocarbon products whereb carbonaceousmaterial is deposited on said pebbles; continuously contacting thatportion of said contiguous mass of pebbles flowing thru said pebblecooling zone at an initial pebble temperature in the range of 1300 to2600 F. with a stream of superheated steam at a temperature and flowrate regulated to insure substantially complete removal of carbonaceousdeposit from said pebbles by the water gas reaction and cooling thereofto a temperature between about 500 and about 900 F.; continuouslyremoving pebbles from said pebble cooling zone; continuously introducingpebbles to said pebble heating zone: and continuously recoveringconverted hydrocarbons from said conversion zone.

6. The process of claim 5 in which pebble flow and gas flow in pebbleheating zone, conversion zone, and pebble cooling zone arecountercurrent,

7. The process of claim 5 in which the pebbles are catalytic withrespect to the conversion reac tion.

8. A continuous process for conversion of hydrocarbons at elevatedtemperatures which comprises continuously flowing a contiguous fluentmass of hot refractory pebbles by gravity thru a series of substantiallyvertically extending zones comprising from highest to lowest a pebbleprebeating zone, a pebble heating zone, a conversion zone, a pebblecooling zone, and several relatively narrow connecting zones forpermitting relatively free flow of pebbles between said zones, all ofsaid zones being substantially fllled with said mass of pebbles;continuously contacting that por tion of said mass of pebbles in saidpebble preheating zone with a stream of gaseous efliuents from saidconversion zone to substantially preheat said pebbles; continuouslycontacting that portion of said mass of pebbles in said pebble heatingzone with a stream of hot combustion gas whereby said pebbles are heatedto a temperature sub- 8 stantially above a predetermined conversiontemperature; continuously contacting that portion of said mass ofpebbles in said conversion zone with a stream of hydrocarbon gas to beconverted at a flow rate regulated to insure maintenance of saidpredetermined conversion temperature and substantial conversion ofhydrocarbon to desired products with concomitant deposition oicarbonaceous material on said pebbles; continuously contacting thatportion of said mass of pebbles in said pebble cooling zone with astream of superheated steam at a temperature and flow rate regulated toinsure substantial removal of said carbonaceous material from saidpebbles by the water gas reaction and substantial cooling thereof withconcomitant production of water gas; continuousl burning said water gasto produce at least a portion of said combustion gas used in the pebbleheatin zone; continuously removing pebbles from said pebble coolingzone; continuously introducing pebbles to said pebble preheating zone;and continuously recovering the eflluents from the conversion zone.

9. The process of claim 8 in which conversion temperature is in therange of about 1500 to 3000 F. and pebble exit temperature from theconversion zone is in the range of about 1300- 2600 F.

10. A continuous process for conversion of hydrocarbons to moredesirable hydrocarbons at elevated temperatures which comprisescontinuously flowing a contiguous fluent mass of hot refractory pebblesby gravity thru a series of substantially vertically extending zonescomprising from highest to lowest a pebble preheating zone, a pebbleheating zone, a conversion zone, a pebble cooling zone, and severalrelatively narrow connecting zones for permitting relatively free flowof pebbles between said zones, all of said zones being substantiallyfilled with said mass of pebbles; continuously contacting that portionof said mass of pebbles in said pebble preheating zone with a stream ofgaseous eilluents from said conversion zone to substantially preheatsaid pebbles; continuously contacting that portion of said mass ofpebbles in said pebble heatin zone with a stream of hot combustion gaswhereby said pebbles are heated to a temperature substantially above apredetermined conversion temperature in the range of 1500 to 3000 F.;continuously contacting that portion of said mass of pebbles in saidconversion zone with a stream of hydrocarbon gas to be converted at aflow rate regulated to insure maintenance of said predeterminedconversion temperature and substantial conversion of hydrocarbon todesired hydrocarbon products with concomitant deposition of carbonaceousmaterial on said pebbles; continuously contacting that portion of saidmass of pebbles in said pebble cooling zone at an initial pebbletemperature in the range of 1300 to 2600 F. with a stream of superheatedsteam at a temperature and flow rate regulated to insure substantiallycomplete removal of said carbonaceous material from said pebbles by thewater gas reaction and cooling thereof to a temperature in the range of500 to 900 F.; continuously removing pebbles from said pebble coolingzone; continuously introducing pebbles to said pebble preheating zone;and continuously recovering the converted hydrocarbons from theconversion zone.

11. In a process of converting hydrocarbons at .elevated temperatures todesirable products wherein a fluent contiguous mass of refractorypebbles is circulated by gravity thru a series oi.

zones comprising a pebble heating' zone and a I conversion zonecommunicating thru a relatively narrow elongated zone and permittingrelatively free flow of pebbles therethru, said zones beingsubstantially filled with said mass 01' pebbles? wherein that portion ofsaid mass or pebbles flowing thru said pebble heating zone iscontinuously Q pebble heating zone I with-a stream of hot combustion gasto heat said v pebbles to a temperature substantially above apredetermined conversion temperature in the I range of 1500 to 3000 F.and that portion of said mass of pebbles flowing thru said conversionzone is continuously contacted with a stream of hydrocontacted with astream of hot combustion gas to heat said pebbles to a temperaturesubstantially above a predetermined conversion temperature and thatportion of said mass of pebbles flowing thru said conversion zone iscontinuously contacted with a stream of hydrocarbons to heat and convertthe same to desirable products; and

wherein carbonaceous matter is deposited on said pebbles in saidconversion zone; the improvement which comprises flowing said mass ofpebbles from said conversion zone thru a pebble cooling zone and therecontinuously contacting said mass of pebbles with a stream of steam at atemperature and flow rate regulated to insure substantial removal ofsaid carbonaceous matter from said pebbles by the water gas reaction andsub- I carbons to heat and convert the same to desirable hydrocarbonproducts; and wherein carbonaceous matter is deposited on said pebblesin said conversion zone; the improvement which comprises flowing saidmass of pebbles from said conversion z'onethru 'a pebble cooling zoneseparated from said conversion zone and there continuously con tactingsaid mass of pebbles at an initial pebble temperature in the range of1300 to 2600 F. with a stream of steamat a temperature and flowrate,z11lated to insure substantially complete re- I range of 500 to 900 F.

stantial coolingv of said pebbles and continuously burning the water gasproduced to form at least a portion of said hot combustion gas. 1

12. In a process of converting hydrocarbons to more desirablehydrocarbons at elevated-temperatures to desirable products wherein afluent contiguous mass of refractory pebbles is circulated by gravitythru a series of zones comprising a 1 pebble heating zone and aconversion zone communicating thru a relatively narrow elongated zoneand permitting relatively free flow of pebblestherethru, said zonesbeing substantially filled with said mass or pebbles; wherein thatportion of said mass of pebbles flowing tbru said moval of saidcarbonaceous matter from said pebbles by the water gas reactionand'substantiallycooling of said pebbles to a-temperature in the HARRISA. BUTCHER.

REFERENCES crrEn .The' following'references are of record in the file ofthis patent:

UNITED STATES PATENTS Number I Name Date 1,724,982 Trumble Aug. 20, 19291,875,923 Harrison Sept. 6, 1932' 1,977,684 Lucke Oct. 23, 19342,336,466 Chatterton et al. Dec. 14, 1943 2,389,636 Ramseyer Nov.- 2'7,1945 2,44 ,922

Simpson et al. Sept. 7, 1948 is I continuously contacted

12. IN A PROCESS OF CONVERTING HYDROCARBONS TO MORE DESIRABLEHYDROCARBONS AT ELEVATED TEMPERATURES TO DESIRABLE PRODUCTS WHEREIN AFLUENT CONTIGUOUS MASS OF REFRACTORY PEBBLES IS CIRCULATED BY GRAVITYTHRU A SERIES OF ZONES COMPRISING A PEBBLE HEATING ZONE AND A CONVERSIONZONE COMMUNICATING THRU A RELATIVELY NARROW ELONGATED ZONE ANDPERMITTING RELATIVELY FREE FLOW OF PEBBLES THERETHRU, SAID ZONES BEINGSUBSTANTIALLY FILLED WITH SAID MASS OF PEBBLES; WHEREIN THAT PORTION OFSAID MASS OF PEBBLES FLOWING THRU SAID PEBBLE HEATING ZONE ISCONTINUOUSLY CONTACTED WITH A STREAM OF HOT COMBUSTION GAS TO HEAT SAIDPEBBLES TO A TEMPERATURE SUBSTANTIALLY ABOVE A PREDETERMINED CONVERSIONTEMPERATURE IN THE RANGE OF 1500 TO 3000*F. AND THAT PORTION OF SAIDMASS OF PEBBLES FLOWING THRU SAID CONVERSION ZONE IS CONTINUOUSLYCONTACTED WITH A STREAM OF HYDROCARBONS TO HEAT AND CONVERT THE SAME TODESIRABLE HYDROCARBON PRODUCTS; AND WHEREIN CARBONACEOUS MATTER ISDEPOSITED ON SAID PEBBLES IN SAID CONVERSION ZONE; THE IMPROVEMENT WHICHCOMPRISES FLOWING SAID MASS OF PEBBLES FROM SAID CONVERSION ZONE THRU APEBBLE COOLING ZONE SEPEARTED FROM SAID CONVERSION ZONE AND THERECONTINOUSLY CONTACTING SAID MASS OF PEBBLES AT AN INITIAL PEBBLETEMPERATURE IN THE RANGE OF 1300 TO 2600*F. WITH A STREAM OF STEAM AT ATEMPERATURE AND FLOW RATE REGULATED TO INSURE SUBSTANTIALLY COMPLETEREMOVAL OF SAID CARBONACEOUS MATTER FROM SAID PEBBLES BY THE WATER GASREACTION AND SUBSTANTIALLY COOLING OF SAID PEBBLES TO A TEMPERATURE INTHE RANGE OF 500 TO 900*F.